Infectious Diseases Practice Questions

Q: What is the commonest age group for infant botulism?

2 to 4 months. **Explanation:** Infant botulism is caused by the ingestion of *Clostridium botulinum* spores (commonly from honey or environmental soil/dust), which germinate and produce toxins in the immature intestinal tract of infants. **Why 2 to 4 months is correct:** While infant botulism can occur between 1 week and 12 months of age, the **peak incidence is between 2 and 4 months**. This specific window corresponds to the period when the infant’s intestinal microflora is still developing and the gastric acidity is relatively low, providing an ideal environment for spore germination and toxin production. By the time an infant reaches the latter half of their first year, a more mature gut microbiome provides "colonization resistance," making it harder for *C. botulinum* to establish itself. **Analysis of Incorrect Options:** * **A (1 to 3 weeks):** Though possible, it is rare. Most cases require a period of environmental exposure and a specific stage of gut maturation that typically peaks later than the neonatal period. * **C & D (7 to 12 months):** As infants grow older and start solid foods, their intestinal flora becomes more diverse and protective. The risk significantly declines after 6 months of age. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** "Floppy Baby" syndrome—characterized by constipation (often the first sign), weak cry, poor sucking reflex, and symmetric descending paralysis. * **Source:** Honey is the most identified dietary reservoir; hence, it is contraindicated for children under 1 year. * **Diagnosis:** Identification of *C. botulinum* spores or toxin in the **stool** (toxin is rarely found in the blood in infant botulism, unlike foodborne botulism). * **Treatment:** Intravenous **Botulism Immune Globulin (BabyBIG)**. Avoid antibiotics (like aminoglycosides) as they may worsen paralysis by releasing more toxin.

Q: What is the most common bacteria causing diarrhea in children?

Enteropathogenic E.coli. **Explanation:** Diarrhea remains a leading cause of morbidity and mortality in children worldwide. While **Rotavirus** is the most common *viral* cause, **Enteropathogenic E. coli (EPEC)** is recognized as the most common *bacterial* cause of diarrhea in children, particularly in infants and those in developing countries. **Why EPEC is the correct answer:** EPEC is a major cause of infantile diarrhea. It works through an "attachment and effacement" mechanism, where it adheres to intestinal epithelial cells using a bundle-forming pilus (bfp) and destroys the microvilli. This leads to malabsorption and watery diarrhea. It does not produce toxins, unlike other strains. **Analysis of Incorrect Options:** * **Enterotoxigenic E. coli (ETEC):** This is the most common cause of **Traveler’s diarrhea** in adults and children. It produces Heat-labile (LT) and Heat-stable (ST) toxins. * **Enteroinvasive E. coli (EIEC):** This strain invades the colonic mucosa, causing a syndrome similar to Shigellosis (dysentery with blood and mucus). It is less common than EPEC in the pediatric age group. * **Enterohemorrhagic E. coli (EHEC):** Specifically serotype O157:H7, it produces Shiga-like toxins. It is associated with **Hemolytic Uremic Syndrome (HUS)** and bloody diarrhea, but it is not the most common bacterial cause overall. **Clinical Pearls for NEET-PG:** * **Most common cause of diarrhea (Overall):** Rotavirus. * **Most common bacterial cause (Children):** EPEC. * **Most common bacterial cause (Adults/Travelers):** ETEC. * **Persistent Diarrhea in HIV:** Cryptosporidium parvum. * **Rice Water Stools:** Vibrio cholerae. * **Management Gold Standard:** Oral Rehydration Salts (ORS) and Zinc supplementation (20mg/day for 14 days; 10mg for infants <6 months).

Q: A 2-year-old girl presents with recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation, and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. What is the most likely diagnosis?

HIV infection. ### Explanation The clinical presentation of this 2-year-old girl is highly suggestive of **Pediatric HIV infection**. The diagnosis is based on a constellation of chronic, multi-systemic findings: 1. **Failure to Thrive (FTT):** Her weight (6 kg) is significantly low for her age and height (78 cm), indicating severe wasting. 2. **Opportunistic & Recurrent Infections:** Resistant oral thrush (Candidiasis) and chronic/recurrent diarrhea (often due to *Cryptosporidium* or *Isospora*) are hallmark signs of immunodeficiency. 3. **Physical Findings:** Hepatosplenomegaly and perianal excoriation (secondary to chronic diarrhea) are common clinical markers in pediatric HIV. **Analysis of Incorrect Options:** * **A. Necrotizing enterocolitis:** Typically occurs in preterm neonates in the first few weeks of life, presenting with abdominal distension and pneumatosis intestinalis, not chronic FTT and thrush. * **B. Lactose intolerance:** While it causes osmotic diarrhea and perianal excoriation, it does not explain hepatosplenomegaly, resistant thrush, or severe systemic wasting. * **D. Campylobacter jejuni:** Causes acute bloody diarrhea (dysentery), but it is a self-limiting or acute bacterial infection and doesn't account for the chronic multi-organ involvement. **NEET-PG High-Yield Pearls:** * **Cardinal Signs:** Suspect HIV in children with "The Triad": Chronic diarrhea, Failure to Thrive, and Persistent Lymphadenopathy/Hepatosplenomegaly. * **Diagnosis:** In children ** 18 months**, **ELISA** is used. * **Most Common Opportunistic Infection:** *Pneumocystis jirovecii* pneumonia (PCP) is the most common opportunistic infection in HIV-infected infants, peaking between 3–6 months of age. * **WHO Clinical Staging:** Oral candidiasis and unexplained persistent diarrhea for >1 month place the child in Clinical Stage 3 or 4.

Q: What is the most common complication of malaria in children?

Severe malarial anemia. **Explanation:** In pediatric populations, particularly in high-transmission areas (Sub-Saharan Africa and parts of SE Asia), **Severe Malarial Anemia (SMA)** is the most frequent manifestation of severe *Plasmodium falciparum* infection. **Why Severe Malarial Anemia is the correct answer:** The pathogenesis involves a triad of: 1. **Direct Parasitization:** Destruction of infected RBCs during schizogony. 2. **Splenic Sequestration:** Removal of both infected and non-infected RBCs by the spleen. 3. **Dyserythropoiesis:** Bone marrow suppression mediated by inflammatory cytokines (TNF-α), which inhibits the production of new RBCs. In children, who have lower iron stores and higher growth demands, this leads to a rapid and profound drop in hemoglobin. **Analysis of Incorrect Options:** * **Cerebral Malaria (A):** While it is the most common cause of **death** and the most dramatic presentation, it is statistically less frequent than anemia in children. * **Respiratory Distress (B):** Often caused by metabolic acidosis (Kussmaul breathing) or pulmonary edema, it is a significant predictor of mortality but occurs less frequently than SMA. * **Hypoglycemia (D):** A common metabolic complication due to parasite glucose consumption and quinine therapy, but it is secondary to the hematological impact. **NEET-PG High-Yield Pearls:** * **Most common complication in children:** Severe Malarial Anemia. * **Most common complication in adults:** Acute Renal Failure (ARF) and Jaundice. * **Most common cause of death (overall):** Cerebral Malaria. * **WHO Definition of SMA:** Hemoglobin < 5 g/dL or Hematocrit < 15% in the presence of parasitemia. * **Drug of Choice for Severe Malaria:** Intravenous Artesunate (preferred over Quinine).

Q: Koplik spots are described as:

A manifestation seen before cutaneous rashes but seldom observed.. **Explanation:** **Koplik spots** are the pathognomonic enanthem of Measles (Rubeola). They are described as small, bluish-white grains of sand on an erythematous base, typically found on the buccal mucosa opposite the lower second molars. 1. **Why Option D is Correct:** Koplik spots appear during the **prodromal stage**, usually 48 hours before the onset of the characteristic maculopapular rash. While they are highly specific for measles, they are "seldom observed" in clinical practice because they are transient, appearing and disappearing within 12–24 hours, often before the patient seeks medical attention for the rash. 2. **Why Other Options are Incorrect:** * **Option A:** The first manifestations of measles are the "3 Cs"—Cough, Coryza, and Conjunctivitis—along with high-grade fever. Koplik spots follow these initial symptoms. * **Option B:** They are not "rarely seen" in terms of occurrence (they occur in up to 70-90% of cases); they are simply missed due to their fleeting nature. * **Option C:** Koplik spots precede the rash. They typically start to fade as the cutaneous rash begins to appear. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic:** Koplik spots = Measles. * **Timeline:** Prodromal stage (Day 2-3) → Koplik spots → Exanthematous stage (Day 4: Rash starts behind ears). * **Vitamin A:** Supplementation is recommended for all children with measles to reduce morbidity and mortality. * **SSPE:** Subacute Sclerosing Panencephalitis is a late, lethal neurological complication of measles occurring years later. * **Modified Measles:** Occurs in partially immune individuals; Koplik spots are usually absent here.

Q: Death in poliomyelitis is usually due to?

Respiratory Paralysis. **Explanation:** The primary cause of mortality in Poliomyelitis is **Respiratory Paralysis**. While the majority of polio cases are asymptomatic or mild, paralytic polio occurs in about 1% of infections. Death occurs when the virus affects the motor neurons responsible for breathing. This happens through two main mechanisms: 1. **Bulbar Polio:** The virus attacks the brainstem (medulla oblongata), paralyzing the cranial nerves and the vital respiratory control centers. 2. **Spinal Polio:** High cervical cord involvement leads to paralysis of the **phrenic nerve** (C3-C5), causing diaphragm failure, or involvement of thoracic segments leading to intercostal muscle paralysis. **Analysis of Incorrect Options:** * **Hypertension (A):** While autonomic dysfunction can occur in bulbar polio leading to blood pressure fluctuations, it is rarely the direct cause of death. * **Aspiration (C):** Bulbar involvement causes pharyngeal paralysis and loss of gag reflex, which significantly increases the risk of aspiration pneumonia. While a serious complication, the immediate cause of death in the acute phase is typically the failure of the respiratory pump itself. * **Arrhythmias (D):** Involvement of the cardiovascular centers in the medulla can lead to tachycardia or arrhythmias, but these are secondary to the profound hypoxia caused by respiratory failure. **High-Yield Pearls for NEET-PG:** * **Most common type of Polio:** Inapparent/Asymptomatic infection (91-96%). * **Most common strain causing paralysis:** Type 1 (Brunhilde). * **Eradication status:** Type 2 (1999) and Type 3 (2012) have been globally eradicated. * **Clinical Sign:** "Tripod sign" (inability to sit upright without supporting hands behind the back) indicates meningeal irritation. * **Post-Polio Syndrome:** Occurs 15–40 years after recovery due to the gradual degeneration of remaining motor neurons.

Q: Most cases of post-infection encephalitis follow which of the following?

Measles. **Explanation:** **Post-infectious encephalitis** (also known as Acute Disseminated Encephalomyelitis - ADEM) is an immune-mediated demyelinating disease of the central nervous system that typically occurs 1–2 weeks following a viral infection or vaccination. **Why Measles is the Correct Answer:** Among the childhood exanthematous illnesses, **Measles (Rubeola)** is historically and clinically the most common cause of post-infectious encephalitis. It occurs in approximately 1 in 1,000 cases of measles. The pathogenesis involves an autoimmune attack on the myelin basic protein triggered by the virus, rather than direct viral invasion of the brain parenchyma. It is characterized by sudden onset of fever and neurological deficits during the convalescent phase of the rash. **Analysis of Incorrect Options:** * **Rheumatic Fever:** This is a post-streptococcal (Group A Streptococcus) inflammatory disease affecting the heart, joints, and skin. While it can cause **Sydenham’s chorea** (involving the basal ganglia), it does not typically present as encephalitis. * **Chickenpox (Varicella):** While Varicella can cause neurological complications, the most common presentation is **Acute Cerebellar Ataxia** (post-varicella cerebellitis) rather than generalized encephalitis. * **Mumps:** Mumps is a common cause of **aseptic meningitis** and can cause direct viral encephalitis, but it is statistically less frequent than measles as a trigger for post-infectious ADEM. **NEET-PG High-Yield Pearls:** * **Subacute Sclerosing Panencephalitis (SSPE):** Do not confuse post-infectious encephalitis with SSPE. SSPE is a **late** complication (years later) caused by a persistent mutant measles virus. * **ADEM Pathological Hallmark:** Perivascular "sleeves" of demyelination. * **Most common cause of sporadic viral encephalitis:** Herpes Simplex Virus (HSV-1). * **Most common cause of epidemic encephalitis in India:** Japanese Encephalitis (JE).

Q: A child presents with tuberculosis. Steroids are not indicated in which of the following conditions?

Progressive primary pulmonary disease. **Explanation:** In the management of pediatric tuberculosis, corticosteroids are used as an adjunct to Anti-Tubercular Treatment (ATT) primarily to reduce the inflammatory response and prevent complications like fibrosis or mechanical obstruction. **Why Progressive Primary Pulmonary Disease (PPPD) is the correct answer:** PPPD refers to the direct progression of a primary focus into pneumonia or cavitation. In this condition, the primary requirement is intensive bactericidal action (ATT). Steroids have **no proven benefit** in PPPD and may theoretically interfere with the local immune response required to contain the infection. **Analysis of Incorrect Options:** * **Tuberculoma:** Steroids are indicated if there is significant perilesional edema causing increased intracranial pressure or focal neurological deficits. * **Endobronchial Tuberculosis:** Steroids are used to reduce the inflammatory edema and granulation tissue in the airway, thereby preventing bronchial obstruction and subsequent collapse or bronchiectasis. * **Massive Pleural Effusion:** While not always mandatory, steroids are indicated in massive effusions to hasten the resolution of fluid, reduce systemic symptoms (fever/pain), and prevent pleural thickening/fibrosis. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Indications for Steroids in TB:** TB Meningitis (Stage II and III) and Miliary TB (if associated with respiratory distress or hypoxia). * **Other Indications:** Pericardial effusion (to prevent constrictive pericarditis), severe phlyctenular conjunctivitis, and renal TB (to prevent ureteric strictures). * **Standard Dose:** Prednisolone 1–2 mg/kg/day for 4–6 weeks, followed by a tapering dose.

Question 1

Which of the following statements regarding measles is false?

Accepted Answer

Koplik's spots cannot be seen in conjunctival or vaginal mucosa.

Answer

Vitamin A administration is part of the management of clinical measles.

Answer

CD 150 and PVRL4 are receptors for measles virus.

Answer

Pneumonia is the common cause of death in children with measles.

Question 2

What is the commonest age group for infant botulism?

Accepted Answer

2 to 4 months

Answer

1 to 3 weeks

Answer

10 to 12 months

Answer

7 to 9 months

Question 3

According to NACO guidelines, which of the following is NOT an indication for starting Antiretroviral Therapy (ART) in children?

Accepted Answer

All of the above are indications for ART

Answer

Infants < 11 months with CD4 count < 1500 cells/mm³

Answer

Children 12-35 months with CD4 count < 500 cells/mm³

Answer

Children 36-59 months with CD4 count < 350 cells/mm³

Question 4

What is the most common bacteria causing diarrhea in children?

Accepted Answer

Enteropathogenic E.coli

Answer

Enterotoxigenic E.coli

Answer

Enteroinvasive E.coli

Answer

Enterohemorrhagic E.coli

Question 5

A 2-year-old girl presents with recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation, and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. What is the most likely diagnosis?

Accepted Answer

HIV infection

Answer

Necrotizing enterocolitis

Answer

Lactose intolerance

Answer

Campylobacter jejuni infection

Question 6

What is the most common complication of malaria in children?

Accepted Answer

Severe malarial anemia

Answer

Cerebral malaria

Answer

Respiratory distress

Answer

Hypoglycemia

Question 7

Koplik spots are described as:

Accepted Answer

A manifestation seen before cutaneous rashes but seldom observed.

Answer

The first manifestation of measles.

Answer

Rarely seen in measles.

Answer

Seen 2-3 days after cutaneous rashes.

Question 8

Death in poliomyelitis is usually due to?

Accepted Answer

Respiratory Paralysis

Answer

Hypertension

Answer

Aspiration

Answer

Arrhythmias

Question 9

Most cases of post-infection encephalitis follow which of the following?

Accepted Answer

Measles

Answer

Rheumatic fever

Answer

Chicken pox

Answer

Mumps

Question 10

A child presents with tuberculosis. Steroids are not indicated in which of the following conditions?

Accepted Answer

Progressive primary pulmonary disease

Answer

Tuberculoma

Answer

Endobronchial tuberculosis

Answer

Massive pleural effusion

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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